The BMW116 aircraft engine primarily was designed to fill the need for a medium-powered vee-type engine for advanced training planes in which pilots could gain experience before passing to first-line fighting planes equipped with high-powered vee-type engines. Although little has been heard about this BMW engine it was developed about the same time as the Junkers Jumo 210 which is of the same basic type with inverted water-cooled cylinders. The German Air Ministry chose the Junkers Jumo 210 for training purposes for the Luftwaffe and so the BMW116 never was placed in production.
The field of the medium-powered vee-type engine is an important one and it has been given serious attention in Germany and England. Engines with power outputs of approximately 600 hp are much cheaper to build than engines of 1,200 hp and their fuel and lubricating oil consumption is less. They give an excellent performance to advanced training planes and eliminate tying up first-line planes for training purposes. Furthermore, they reduce danger of crashes as the planes in which they are installed can have lighter wing loadings and lighter power loadings.
The BMW116 engine with its displacement of 1,267 cu in and output of 600 hp at 11,800 ft is in the same category as the junkers Jumo 210 (1,202 cu in displacement and 545 hp at 13,750 ft) and the Rolls-Royce Kestrel (1,296 cu in and 745 hp at 14,500 ft). These engines pinch-hit in training planes for the more powerful Junkers Jumo 211 and Mercedes-Benz DB601 in Germany, and the Rolls-Royce Merlin in England. Here in the United States we do not have an engine in this category with which our pilots can obtain experience before graduating to the Allison.
In design and construction the BMW116 is a conventional vee-type engine with twelve water-cooled cylinders arranged in two inverted banks with an angle of 60 degrees between them. Each cylinder block is attached to the crankcase with fourteen long hold-down studs passing through portions of the block adjacent to the combustion chambers in the cylinders. This arrangement transmits stresses in the cylinder heads direct to the crankcase without the need for flanges on the ends of the cylinders and short studs and nuts.
Two inlet valves and two exhaust valves are provided in each cylinder and they are actuated by overhead camshafts driven by vertical shafts at the rear of the engine. The intake manifolds are attached to the inside of the cylinder blocks and the exhaust openings are on the outside. The carburetor is located between the two blocks close to the intake manifolds so that distribution of mixture is approximately the same to all of the cylinders.
The supercharger is of the gear-driven, one-speed type with a gear ratio of 8.2:1. It has two air intakes equipped with flame traps and a single large manifold leading to the carburetor. The carburetor is of BMW manufacture and is of the multi-jet type with automatic mixture control and altitude control. Its shape and location are such that a multi-unit direct fuel injection pump can be substituted for it without difficulty. When using 87-octane gasoline in the carburetor the fuel consumption of the engine is 0.55 lb/hp/hr at maximum continuous output and 0.50 lb/hp/hr at cruising output.
The ignition system comprises two twelve-cylinder Bosch magnetos mounted on the accessory or rear section of the engine and two Bosch plugs in each cylinder. A Bosch hand and electric starter also is mounted on the accessory section where it can mesh with the rear end of the crankshaft. A tachometer drive is provided above the starter and drives arc provided from the rear ends of the camshafts for vacuum pumps or high-pressure oil pumps. The centrifugal pump for circulating the cooling water is mounted underneath the rear part of the engine.
The propeller drive has spur gears which give it a reduction of 1.54:1 or 1.87:1. The gear housing is integral with the front end of the crankcase. The propeller shaft has the customary flange with eight bolt holes and serrations in accordance with German standards. A shell gun can be mounted to fire through the hollow propeller shaft by removing a cover plate just above the supercharger casing. Two attachments are provided on each side of the crankcase for mounting the engine in the airframe.
When operating on 87-octane gasoline the BMW116 has an output of 600 hp at 3,000 rpm for takeoff and it develops this output at its rated altitude of 11,800 ft. At an altitude of 14,750 ft it has an output of 510 hp at 2,840 rpm. It weighs 1,003 lb dry which is equivalent to a specific weight of 1.67 lb/hp. This is quite a good performance for a medium-powered engine which has not been fully developed. The engine also can be equipped with a two-speed supercharger having gear ratios of 5:1 and 8.2:1 which increases its performance.
In addition to the BMW116, BMW Flugmotorenbau GmbH has also built another engine with inverted water-cooled cylinders. This other engine is considerably larger and is in the same power class as the 1,200-hp Junkers Jumo 211 and Mercedes-Benz DB601. It has not been built in quantities, however, as it is the policy of the German Air Ministry never to have more than two engines of the same type and power output in production.
This article was originally published in the December, 1940, issue of Aviation magazine, vol 39, no 12, pp 84, 152.
The original article includes 2 photos of the engine.
Photos are not credited.